U.S. President Barack Obama walks from Marine One as he returns to the White House on May 9, 2014 in Washington, DC. (Allison Shelley/Getty Images North America)

As Barack Obama enters the twilight of his tenure, the ­debate over his legacy is ­beginning, but one conclusion already seems certain. It can best be described as “Honey, I shrunk the presidency.”

Not since Jimmy Carter was held hostage by Iran has the Oval Office seemed so inconsequential against the forces of international darkness. The mismatch is particularly striking because smallness has been Obama’s choice.

Although he is guilty of executive overreach at home, that bully behavior only sharpens the contrast with a foreign policy that is feeble when it is not comatose. The president’s estrangement from the demands of global leadership is giving a green light to tyrants and malevolent opportunists everywhere.

His preference for navel gazing over action was on full display last week. As Russia and China menaced their neighbors and Islamist terrorists set off bombs in a half-dozen countries, Obama accepted an award from Hollywood pal Steven Spielberg for fighting genocide. Passing up a chance to give a full-throated defense of freedom and Western civilization, the president lapsed into what The New York Times called a “meditation” on the limits of his power.

That’s far too kind. It was a white flag of surrender and more proof that Obama lacks the capacity to shoulder the responsibilities that have belonged to the Oval Office for 100 years.

The speech sounded like that of a man who is shocked to find that evil still roams the Earth, and doesn’t have a clue what to do about it. A long paragraph of his meandering remarks, released by the White House, captures his sense of helplessness.

“I have this remarkable title right now — president of the United States — and yet every day when I wake up, and I think about young girls in Nigeria or children caught up in the conflict in Syria — when there are times in which I want to reach out and save those kids — and having to think through what levers, what power do we have at any given moment, I think, ‘drop by drop by drop,’ that we can erode and wear down these forces that are so destructive, that we can tell a different story,” Obama said.

If there was a course of action buried in that litany of woe, it ­escapes me. The sequence amounts to a counsel of defeat.

Earlier, he had talked about rising anti-Semitism and the spread of sectarian and tribal conflicts.

“We cannot eliminate evil from every heart, or hatred from every mind,” he said. “But what we can do, and what we must do, is make sure our children and their children learn their history so that they might not repeat it. We can teach our children the hazards of tribalism. We can teach our children to speak out against the casual slur. We can teach them there is no ‘them,’ there’s only ‘us.’ ”

There you have it. We can teach our children warm and fuzzy things — assuming they and we are not killed by madmen first. In which case, there’s nothing we can do.